In recent years, high density recording media have been increasingly employed in magnetic tapes for general use, e.g., for audio recording, video recording and, computer applications. To provide high density recording media for such applications, more finely grained conventional Co-containing magnetic iron oxides have been used.
In addition, ferromagnetic alloy powders can be used, as well as ferromagnetic metal thin film magnetic recording media which are formed using vapor deposition methods such as vacuum evaporation, sputtering, or ion plating. These media have recently attracted considerable attention, and are now in practical use.
In high-density magnetic tapes for audio, video or computer applications, the surface of the magnetic layer is smoothed in order to improve sensitivity (i.e., output, particularly in the high frequency region). On the other hand, for various purposes, e.g., imparting antistatic property, a backing layer is provided on the opposite side of a non-magnetic support to the side where the magnetic layer is provided. For example, a backing layer containing carbon black is described in U.S. Pat. No. 4,310,599. When the magnetic layer is finished so as to have a smooth surface, however, the improvement in sensitivity is limited due to the roughness of the backing layer.
In addition, it is desirable to produce magnetic tapes having the least possible total thickness, and in many cases magnetic tapes have a thickness of only about 20 .mu.m or less.
With the reduction of the total thickness, the backing layer of such tapes is also reduced, often to a thickness of 2 .mu.m or less. However, such a thin backing layer tends to be pared.
The reduction in total thickness of such magnetic tapes has the disadvantage that mechanical strength of the magnetic tape is reduced, accompanied by poor running durability, winding characteristics, and output fluctuation.